1. Field of the Invention
The present invention relates to a fiber-optic reflective displacement micrometer and, in particular, to a multi-range fiber-optic reflective displacement micrometer which can arbitrarily change measuring ranges to measure a displacement and its relevant physical quantities such as surface roughness and flatness.
2. Description of the Related Art
The conventional fiber-optic reflective displacement micrometer is constructed by directing light from a light source through a transmitting optical fiber to an object whose displacement is to be measured and then measuring the amount of light reflected from the surface of the object so as to obtain the displacement of the object. For compensating the fluctuations in the intensity of the light and the reflectivity of the surface of the object, a method of utilizing a light from a reference optical fiber and one utilizing a ratio resulting from two receiving optical fibers are ever adopted.
However, the above conventional fiber-optic reflective displacement micrometer has some drawbacks as the follows. Firstly, the resolution of the conventional fiber-optic displacement micrometer is only at the degree of sub-millimeter and thus is not able to perform a measurement for a tiny displacement. Secondly, the measuring scope of the prior art micrometer is very small and thus is only suitable for a measurement for a short-distance displacement.
To obtain a larger measuring range, a fiber-optic reflective displacement micrometer incorporating with a number of lenses, such as U.S. Pat. No. 5,068,527, has ever been proposed. However, such a micrometer is very complicated.
An object of this invention is to provide a multi-range fiber-optic reflective displacement micrometer which has a resolution in the degree of sub-micrometer and a measuring range up to several millimeters or centimeters.
Another object of this invention is to provide a multi-range fiber-optic reflective displacement micrometer whose measuring range can be changed by a change in the quantity of the receiving optical fibers so as to meet need for displacement measurement or one for surface flatness in different ranges.
To achieve the above objects, the present invention discloses a multi-range fiber-optic reflective displacement micrometer comprising:
a light-source for emitting a beam to a surface of an object;
a receiving fiber-optic array including a plurality of receiving optical fibers parallel to each other so as to sample a light reflected from the surface of the object and to output a sampled light therefrom;
a photo-detector array including a plurality of optic-receivers corresponding in quantity to the receiving optical fibers so as to receive the sampled light output from the corresponding receiving optical fiber and to output an electric signal corresponding to the sampled light; and
a processor for producing a measured value representative of the displacement of the object in accordance with the electric signals output by the photo-detector array.
By means of the above structure, the measuring range of the displacement micrometer could be extended by a change in the quantity of the receiving optical fibers located in a region the reflected light could sweep and by a corresponding change in the quantity of the photo-detector.
In a preferred embodiment, the measured value representative of the displacement of the object is derived from a ratio of a differential signal to a composite signal both derived from two adjacent receiving optical fibers which have stronger sampled light. Since such a ratio corresponds to a sectional displacement of the object to be measured, the displacement to be measured is thus extensible with a resolution in the degree of deep-sub-micrometer and such the measurement of the displacement is free to be affected by the fluctuations in the intensity of the light-source and in the property of the reflecting surface.
The above and other objects, features and advantages will become apparent from the following detailed description of preferred embodiments in conjunction with the accompanying drawings.